There are also other possibilities to calculate the three–propagator integrals, like
hypergeometric methods [1]}, [2]} and/or the use of one Mellin–Barnes integral [3]}.
In all these represenations one has to maintain the distribution chatacter of these integrals
in all intermediary steps, which can be technically demanding. The IBP method, on the other hand,
maintains the propagator structure in all these respects and is therefore the method of choice
in the following.
